June 20, 2020

ECOLOGY EPIDEMIOLOGY AND EVOLUTION OF PARASITISM IN DAPHNIA PDF

1 Introduction to the Ecology, Epidemiology, and Evolution of Parasitism in Daphnia. This chapter provides a short introduction to the topic of the book. I define. 7 Host Range of Daphnia Parasites. In this chapter, I summarize what we know about parasite host ranges and host specificity. I outline the ecological. 5 The Effects of Daphnia Parasites on Host Fitness. Parasites use their hosts to foster their own needs, thus interfering with the hosts’ survival and reproduction.

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In vaphnia chapter, I summarize what we know about parasite host ranges and host specificity. I outline the ecological, epidemiological, and taxonomic considerations relevant for assessing host ranges and discuss the problems with describing host ranges in field studies, where the investigation of host ranges is hampered by low statistical power, and laboratory studies, where the absence of evidence is not necessarily evidence for absence.

I argue that Daphnia parasites are generally more specific than thought previously. Every parasite has a host, but no parasite Parasite: Organism exhibiting an obligatory, detrimental dependence on another organism its host. Conceptually, parasite and pathogen are the same. Ectoparasites live on the surface of the host. Moreover, parasites are usually very limited in the number of host species they are able to infect.

Ecology, epidemiology, and evolution of parasitism in Daphnia by Dieter Ebert

Thus, in describing a parasite’s host range, one defines its niche. This description usually resembles a list of host species that a parasite is able to infect. The description of the host ov usually does not distinguish the degree to which a parasite is able to infect a host and which hosts it prefers to infect.

Therefore, the host range, presented as a list of potential host species, cannot tell us much about the evolution and ecology of a parasite, nor about its consequences for the host. Nevertheless, the host range can be, at least locally, a useful tool for identifying certain parasite species and can sometimes even help identify host species by the presence of their specialist parasites.

Describes the observation that only a subset of hosts is susceptible to infection. A high specificity refers to the observation that only a few host lines can be infected by oc given parasite. This term is often used together with host range, such that a wide host range indicates a low specificity. However, although host range is often described as a list of potential host species, specificity is often used to describe host—parasite associations from a more quantitative dapnhia, e.

Host specificity is very important for both ecological and evolutionary aspects of host—parasite interactions. Biologically speaking, any difference in the degree to which a parasite is associated with different host species indicates some degree evolytion specificity. Thus, specificity may range from extreme forms, such as the psrasitism of a parasite to infect only certain members of one host species, to slight differences parasitixm the degree to which the parasite infects or harms different host species.

To gain a deeper understanding of a particular system, it is also helpful to take into account the consequences of specificity for the host and for the parasite. For ecological and evolutionary questions, it is also important to consider from whose point of view one considers specificity. For a parasite, a host is suitable if the parasite is able to reproduce in and transmit from this host species.

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Hosts that do not allow for secondary infections are of little relevance for the parasite’s host range, although the interaction may still be detrimental to the host. A host’s perspective is different. Evolutuon host is part of a host range if it can be infected by the daphnnia, even if the parasite does not do well in this host.

Ecologically, this difference in perspective can be important when considering the spread of parasites and the coexistence of host species. In his review of ” Parasites Parasite: Organism that lives attached to the body surface of another organism.

Ecology, Epidemiology, and Evolution of Parasitism in Daphnia

off Sometimes regarded as ecto-parasites. In zooplankton, epibionts are often ciliates, algae, bacteria, and fungi. Order of the Entomostraca. They have a bivalve shell covering the body but not the head, four evooution six pairs of legs, and two pairs of antennae used for swimming. They mostly inhabit dphnia water. Trans Zool Soc Lond Freshw Biol It is clear that we need more studies to reach a general conclusion on this point.

We currently know little about the parazitism ranges and host specificity Specificity: When investigating potential hosts, one must consider a number of questions whose answers are not as clear-cut as the relative ease of studying host specificity in Daphnia might suggest.

However, this complexity allows us to dig deeper into aspects of host range evolution Evolution: Changes in allele frequencies over time. Before I discuss how to estimate host specificity, I will briefly outline some problems that are important from an evolutionary perspective.

Results from field and laboratory studies suggest that infections xaphnia often highly dependent on the host clones, on the population Population: Group of interbreeding epdiemiology and their offspring.

In asexual species, this definition cannot be applied; in this case, a population is a group of phenotypically matching individuals living in the same area. Thus, statements about host specificity must take into account variation within and between species and even within populations. For example, Pasteuria ramosa shows very strong host clone—parasite isolate interaction.

Within populations, different clones of D. Potential for coevolution and frequency-dependent selection. On the other hand, P. J Anim Ecol Thus, a conservative approach would classify P. Genetic composition of an organism as distinguished from its physical appearance phenotype. The reason for this discrepancy is currently not clear. One possibility is that the P. However, the epidemiolgy, that single P. These two hypotheses can be easily distinguished experimentally.

From an ecological perspective, host specificity may not only be defined by the ability of the parasite to infect a host but also by its effect on the host. For example, Caullerya mesnili paarsitism able to infect D. Morbidity and mortality of a host that is caused by parasites and pathogens. More specifically, it is the fitness component of the parasite that is associated with the harm done to the host.

Because parasites are usually not very rich in morphological characters, it is easy to pool different species into one taxon. It seems likely to me that many currently described parasite species will turn out to be a group of species. A practical way to judge a parasite’s Parasite: This method, however, is rather conservative.

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Using the appropriate statistical test, she found firm support for specificity for only one parasite species. Some of the other parasite species that had appeared to be host specific occurred only rarely or were found only when the other host species was absent, which made a proper comparison impossible.

Stirnadel and Ebert Stirnadel HA, Ebert D Prevalence, host specificity and impact on host fecundity of microparasites and epibionts in three sympatric Daphnia species. Gurleya vavrai was the only parasite unambiguously classified as specific infecting D. Some parasites appeared specific in one pond but unspecific in another pond. Whether these findings are explained by local genetic differences or misidentification of parasites o of cryptic species epivemiology not clear.

Again, low statistical power for the less common parasites prevented us from reaching firm conclusions for a number of epidemiooogy species.

A slightly different approach was used by Bengtsson and Ebert Bengtsson J, Ebert D Distribution and impacts of microparasites on Daphnia in a rockpool metapopulation. Which factors explain parasite richness?. Group of partially isolated populations belonging to the same species. Migration among subpopulations is important for the ecological and evolutionary dynamics of a metapopulation. In these studies, specificity was judged on replication across numerous rock pool populations.

If two Daphnia species occur together in a number of rock pools and one of them is significantly more often infected by a certain parasite species, one may conclude that the parasite is specific to this host.

However, the microsporidium Larssonia sp. Extent to which an individual contributes its genes to future generations in relation to the contribution of other genotypes in the same population at the same time.

Spirobacillus cienkowskii and Larssonia sp. The numerous epibiont species found in rock-pool Daphnia infected all available host species and were even seen to colonize hosts from other taxa, e.

For the other parasites, no clear statement could be made. The available evidence suggests that Daphnia parasites Parasite: Host ranges indicate only the number of host species a certain parasite species is able to infect and can include anything from one to many host species, as well as hosts of different genera or families.

Because the current statistical methods are conservative and some parasites are rare, I believe that more detailed investigation will reveal more examples of specific parasites. Laboratory experiments can best elucidate the host range of parasites with well-defined transmission Transmission: The process by which a parasite passes from a source of infection to a new host.

Horizontal transmission is transmission by direct contact between infected and susceptible individuals or between disease vectors and susceptible individuals. Vertical transmission occurs when a parent conveys an infection to its unborn offspring, as in HIV in humans.

Parasites that do not transmit horizontally under controlled conditions must be studied by field observation. Print view The Book: Epidemillogy you always wanted to know about parasitism in Daphnia.